A. Field of the Invention
The invention relates to the field of fluid spraying and more particularly to blow lance assemblies used in the treatment of molten material.
B. The Prior Art
Thermal treatment of molten material, such as metal, stone, slag, or the like, may include a gas conducting tube or lance to blow reaction gases onto the surface of the molten bath. For example, in steel-making, a lance may supply combustion gas or gases to sustain the oxidation process by which slag and steel are separated in a steel converter. A lance typically contains a central nozzle through which high pressure gas (e.g., greater than 10 barr) passes and which is surrounded by outer flow ports through which flows a further gas or gas mixture. The outer gas or gas mixture usually flows at a relatively lower volume rate than flow through the central nozzle. Since these lances are employed adjacent molten baths, they are usually provided with a water cooling system. In order to save energy, the exterior diameter of the lance is held to be as small as possible. Because gases conducted through the lance are combustible or support combustion, care must be taken in the design of the lance that ignitible mixtures do not form within the lance or that ignitible mixtures which do form are not ignited within the lance.
A known lance assembly for blowing gases against the surface of a molten metal bath is shown in German LP No. 845,643. There, a central nozzle is arranged perpendicularly to the bath surface and is surrounded by a ring of further nozzles whose axes extend radially outward at an angle from the central nozzle axis in the direction of fluid flow from the lance. The central nozzle delivers a relatively high volume flow rate of oxygen or oxygen-enriched air; whereas the diverging further nozzles conduct a slower flow of air or inert gas. The concentric arrangement of diverging nozzles serves to displace the layer of slag floating on the surface of the molten metal, thereby exposing the bare bath surface into direct contact with the central gas jet. All the nozzles are contained in a nozzle block which is equipped with flow channels for the passage of a cooling medium. A drawback with the lance as shown in German LP No. 845,643 is that the fixed cross-sectional area for the central nozzle limits the environments in which the lance assembly can be utilized. A further disadvantage arises in that the central gas flow cannot react with or be supplemented by the surrounding gas flows when the central gas strikes the bath surface.